Researchers at Purdue University have developed a rapid electrokinetic patterning technique that, according to the university, uses a laser and holograms to precisely position numerous tiny particles within seconds. This represents a potential new tool to analyze biological samples or create devices using nanoassembly. The technique is presented as a potential alternative to existing technologies because, as reported by mechanical engineering doctoral student Stuart J. Williams, the patterns can be more quickly and easily changed.

According to a report by the university, the experimental device consists of two parallel electrodes made of indium tin oxide that are spaced 50 micrometers apart. A liquid sample containing fluorescent beads is then injected between the two electrodes, a laser in the near infrared range of the spectrum is shined through one of the transparent electrodes, and a small electrical voltage is applied between the two electrodes. The researchers send holograms of various patterns through this and, because they are holograms, they can create different shapes, such as straight lines or L patterns.

The particles in the liquid sample automatically move to the location of the light and assume the shape of the hologram, which according to the report means the method could be used to not only move particles and molecules to specific locations, but also to create tiny electronic or mechanical features. The light slightly heats the liquid sample and the electric field applied to the plates acts on these altered properties, causing a microfluidic vortex of circulating liquid between the two plates. According to the researchers, this vortex enables researchers to position the particles in the circulating liquid by moving the laser light.

"You could take one particle, a hundred particles or a thousand particles and move them anywhere you want in any shape that you want," Williams said in the report. He added that if a researcher wants to study particles of two different types, he or she can sort one group out and keep the other behind. The system could allow researchers to design sensor technologies that move particles to specific regions on an electronic chip for detection or analysis. Researchers are reportedly trying to develop chips that have a high throughput capability.

The researchers recorded videos of the circulating particles to document the effect. The videos demonstrated how the method could be used to cause particles to stick permanently to a surface in a single crystalline layer, a structure that could be used in manufacturing. The technique is used to move fluorescent-dyed beads of polystyrene, latex and glass, in sizes ranging from 50 nanometers down to 3 micrometers.

The research is based at the Birck Nanotechnology Center in Purdue's Discovery Park. The students won a research award for their work in October during the 12th International Conference on Miniaturized Systems for Chemistry and Life Sciences in San Diego. Findings also have been recently published in two peer-reviewed journals, Lab on a Chip and Microfluidics and Nanofluidics.